1. Field of the Invention
The present invention relates to a burner having a swirl generator and mixing tube.
2. Discussion of Background
A conical burner consisting of several shells, a so-called double-cone burner, for generating a closed swirl flow in the cone head has been disclosed by U.S. Pat. No. 4,932,861 to Keller et al. In this type of burner, the swirl flow becomes unstable on account of the increasing swirl along the axis of the cone and changes into an annular swirl flow with backflow in the core. Fuels, for example, gaseous fuels, are injected along the ducts, also called air-inlet slots, formed by the adjacent edges of the individual adjacent shells and are mixed homogeneously with the air before the combustion occurs by ignition at the stagnation point of the backflow zone or backflow bubble, which is utilized as a flame retention baffle. Liquid fuels are preferably injected via a central nozzle at the burner head and then vaporize in the conical hollow space. Under typical gas-turbine conditions, the ignition of these liquid fuels occurs early near the fuel nozzle, whereby a sharp increase in the NOx values precisely on account of this lack of premixing cannot be avoided, which necessitates, for example, the injection of water. Furthermore, it was found that the attempt to burn hydrogenous gases similar to natural gas led to problems of premature ignition at the gas bores with subsequent overheating of the burner. An attempt has been made to remedy this by a special injection method for such gaseous fuels being introduced at the burner outlet, the results of which, however, have not been completely satisfactory.